The overall objective of this project is to elucidate the neural mechanisms controlling gonadotropin secretion in the rat and to examine how ovarian steroids modulate these mechanisms to account for normal LH and FSH concentrations. With regard to tonic LH secretion, the neural sites at which steroids act to decrease LH-pulse frequency will be determined. Focusing on changes in pulse frequency will insure that neural, rather than pituitary, actions are monitored. The role of the hypothalamus in tonic FSH secretion will also be examined. In particular, I will determine if the dorsal anterior hypothalamic area contributes to FSH secretion during the estrous cycle; the inputs from this area to the medial basal hypothalamus will also be examined. Finally, the hypothesis that the preovulatory gonadotropin surge is initiated by a signal from the suprachiasmatic nucleus which activates a steroid-responsive neural network in the preoptic area will be tested by examining the anatomical and functional connections between these areas. Techniques include radioimmunoassays of LH, FSH, estradiol, and progesterone; controlled delivery of physiological steroid concentrations; a variety of stereotaxic procedures including deafferentation, radiofrequency lesioning, and electrical stimulation; and the tracing of neural pathways using horseradish peroxidase histochemistry and tritiated amino acid autoradiography. The results should provide new insight into the effects of estradiol and progesterone on the brain and the interactions between the ovary and the hypothalamus that determine the timing and rate of ovulation.